Living bodies are exposed to a variety of environmental impacts. Such impacts are almost unlimited in number, including not only physical stimulations such as unceasingly arriving cosmic rays, radiations from the ground surface or buildings, ultraviolet rays in the sunlight and changes in ambient temperature but also chemical stimulations due to absorption of trace polutants in the air or foreign substances in foods and biological invasions by invisible viruses, bacterial, fungi, etc. Each living body is endowed with a very sophisticated and potent protection mechanism and it is this protection mechanism that allow the living organism to survive while overcoming those variegated invasions.
Fundamentally, the mechanism of living body damage by oxidative invasions from the environment and the defense mechanism are common in many aspects irrespective of differences in environmental factors. Thus, it is known that radiation damages, oxidant damages, inflammations, immunization, aging, carcinogenesis and various enzymatic processes are associated with free radical formation or active oxygen. It is also known that when many drugs act in human bodies, their metabolic processes involve free radical formation as a part thereof. Free radical formation is generally a factor harmful to healthy tissues except for its usefulness in some cases, for example in the case of microbicidal action of leukocytes or activation of certain enzymes in which .O.sub.2.sup.- (superoxide radical) is physiologically involved. Living bodies have a nonspecific defense system against such free radical formation. More in detail, when a living body is exposed to a radiation or oxidant or to an action of a drug, such agent not only directly damages substances of biological importance, such as DNA, but also reacts with O.sub.2 in the air to produce .O.sub.2.sup.- or reacts with water (H.sub.2 O) in a tissue to form strongly reactive radicals such as .OH (hydroxy radical). The .O.sub.2.sup.- radical is partly eliminated as a result of conversion to H.sub.2 O.sub.2 by SOD (superoxide dismutase) occurring in tissues. While catalase converts H.sub.2 O.sub.2 to water and oxygen, H.sub.2 O.sub.2 also reacts with .O.sub.2.sup.- to form .OH, which has very high reactivity and attacks a variety of living-body substances. In particular, these reactions, via formation of lipid radicals, lead to peroxidation of unsaturated fatty acid components of phospholipids which are constituents of biomembranes. It is vitamin E that plays a definite role in blocking chain reactions involving those free radicals that are formed from such membrane lipids. When subjected to lipid peroxidation, biomembranes undergo polymerization and their functions are thereby disturbed. This results in temporary inhibition of different biochemical reactions or in abnormalities in the adrenocortical hormone activities. Damages of biomembranes due to the formation of lipid peroxides are prevented by the peroxide eliminating action of the glutathione (GSH)-peroxidase system (GP system).
As mentioned above, living organisms are subjected to various oxidative invasions from outside and inside. At the same time, however, the defense mechanism functions in them through the action of vitamin E and the radical- or peroxide-eliminating action of the above-mentioned SOD or GP system, among others. In case this defense mechanism fails to function satisfactorily, long-term effects of said invasions will result in such general phenomena as ischemic disorders of the brain or heart, damages of the lung and aging of cells. Such various radicals may damage DNA molecules directly and this may lead to carcinogenesis. Furthermore, a number of chemical carcinogens and intermediate metabolites include free radicals themselves or can activate free radicals. Thus, the problem of defense against free radicals and various disorders associated therewith is a problem of protection against carcinogenesis as well.